Writing for telegraph.co.uk, Mr de Bois warned that the current political focus on cutting immigration has meant not enough attention is paid to the impact of emigration.

“Lost in the debate is the enormous damage being done to our economy by migration from the UK,” he said.

Ministers must do more to persuade high-achieving, highly-mobile workers that Britain remains the best place in the world to work and prosper, he said.

“Work needs to begin on keeping people here and not relying on importing others to fill the gap,” he said.

Emphasis added. In my book, importing more talent than you export is brain gain. That's true even if more people are leaving than ever before and the population is in decline. Heeding the advice of Mr. de Bois would do enormous damage to the UK economy.